Field of the Invention
The present invention relates to a vibrator of a vibratory drive unit, a vibratory drive unit, an interchangeable lens, an imaging device, and an automatic stage.
Description of the Related Art
Hitherto, as a linear ultrasonic motor that drives a driven object in a linear manner, a vibratory drive unit (a linear ultrasonic motor) such as the one disclosed in Japanese Patent Laid-Open No. 2004-304887 has been proposed.
The driving principle of such a linear ultrasonic motor will be described with reference to FIGS. 5A, 5B-1, and 5B-2.
As illustrated in an external perspective view of the linear ultrasonic motor in FIG. 5A, a linear ultrasonic motor 510 includes a vibrator 501, a driven body 506, and a pressure applying member (not shown) that presses the vibrator 501 against the driven body 506.
The vibrator 501 includes an electro-mechanical transducer 505, a representative example of which is a piezoelectric element, an elastic body 502 that is formed in a rectangular shape and that is joined to one side of the electro-mechanical transducer 505 in an integrated manner, and two projections 503 and 504 that are formed in a protruding manner with respect to the upper surface of the elastic body 502.
In the ultrasonic motor, voltages of specific frequencies are applied to the piezoelectric element so that desired vibration modes are multiply excited, and by superposing the vibration modes, a driving vibration is formed.
In the motor of FIG. 5A, two bending vibration modes illustrated in FIGS. 5B-1 and 5B-2 are excited in the vibrator 501. Both of the bending vibration modes are bending vibration modes that vibrate in the out-of-plane direction of the plate-shaped vibrator 501.
One of the vibration modes is a second-order bending vibration mode in the longitudinal direction of the vibrator 501 (Mode-A) and the other one of the vibration modes is a first-order bending vibration mode in the traversal direction of the vibrator 501 (Mode-B).
The shape of the vibrator 501 is designed so that the resonant frequencies of the two vibration modes coincide with each other or approach each other. The projections 503 and 504 are disposed near positions that become nodes of the vibration in Mode-A such that, with the vibration in Mode-A, projection end surfaces 503-1 and 504-1 each performs a pendulum motion with the respective node of the vibration as its fulcrum and, accordingly, reciprocates in the X direction.
Furthermore, the projections 503 and 504 are disposed near positions that become antinodes of the vibration in Mode-B such that, with the vibration in Mode-B, the projection end surfaces 503-1 and 504-1 reciprocate in the Z direction.
By simultaneously exciting and superposing the two vibration modes (Mode-A and Mode-B) so that the vibration phase difference between the two vibration modes approaches ±π/2, the projection end surfaces 503-1 and 504-1 each perform an ellipsoidal motion in the XZ plane. With the ellipsoidal motions, the driven body 506 that has been brought into press-contact can be driven to one direction.
Note that if the stiffness of the projections of the vibrator is high, there are cases in which an abnormal noise is generated when the motor is driven.
Furthermore, if the stiffness of the projections is too low, there are cases in which power efficiency and the like decreases.
In order to avert the above, the projections need to have an appropriate stiffness.
Accordingly, as illustrated in FIGS. 6A and 6B, Japanese Patent Laid-Open No. 2011-200051, for example, proposes a vibratory drive unit that is provided with projections that have a spring property.
Projections 5 each include a contact portion 1 that is in contact with a driven unit 8, a spring portion 3 that has a low stiffness in the direction of pressure applied to the vibrating body, and a standing portion 2 that connects the contact portion 1 and the spring portion 3 to each other.
When force is applied to the contact portion 1 in the Z direction, the spring portion 3 that is thinner than a connection portion 4 that is connected to an electro-mechanical transducer is elastically deformed with the boundary between the connection portion 4 as its fulcrum; accordingly, the contact portion 1 and the standing portion 2 is displaced in the Z direction such that a projection with a spring property can be configured.
Other than the above, as a vibrator that is provided with projections that have a spring property, Japanese Patent Laid-Open No. 2011-234608 proposes a vibratory drive unit illustrated in FIGS. 7A and 7B.
As illustrated in FIG. 7B, the projection members 29 each include a cylindrical wall portion 24, a contact portion 26 that includes a contact surface 27 that comes in contact with a driven body (not shown), connection portions 21 that connect the wall portion 24 and the contact portion 26 to each other, and a fixation portion 23 that is fixed on the upper surface of an elastic body 22 by laser welding.
Since the wall portion 24 continues throughout the whole circumference of the projection member 29, the projection member 29 has a high stiffness in the directions defined by the XY plane; accordingly, even if the projection member 29 receives reaction force from the driven body in the X direction during a driving operation, there is little deformation. The boundary between each connection portion 21 and the contact portion 26 is a step so that the driven body does not come into contact with the connection portions 21. Furthermore, the thickness of each connection portion 21 is reduced and the width thereof is reduced by dividing the connection portions 21 into four sections with the hole portions 28; accordingly, the stiffness in the Z direction is reduced such that the connection portions 21 are provided with a spring property.
FIG. 8A is a cross-sectional view illustrating half of the shape of the projection member 29 before and after the deformation when, in the vibrator illustrated in Japanese Patent Laid-Open No. 2011-234608, a pressure is applied to the contact portion 26 of the projection member 29 in the negative direction of the Z-axis.
When a pressure is applied to the contact portion 26 in the negative direction of the Z-axis, the contact portion 26 and the connection portions 21 become deformed. Such a configuration gives the projection member 29 a spring property in the Z direction. If the stiffness of the projection member 29 is high, a beating sound will be generated when the projection member 29 is brought in contact with the driven body, and when the stiffness is low, even if the vibrator is not generating any force in the desired direction, the projection member 29 will be in contact with the slider and efficiency will be degraded.
In order to prevent generation of an abnormal noise and degradation in efficiency, the thickness and the like of each connection portion 21 are set to appropriate values.
As illustrated in FIG. 8B, in the vibrator illustrated in Japanese Patent Laid-Open No. 2011-200051, only the spring portion 3 is mainly deformed. Accordingly, the contact portion 1 and the standing portion 2, in other words, the portion between C and D does not contribute to the spring stiffness.
Accordingly, in order to obtain an appropriate stiffness, the radius R2 of the non-contact portion between the elastic body and the piezoelectric element becomes large. As a result, the adhesion area between the elastic body and the piezoelectric element becomes small, and the elastic body and the piezoelectric element become susceptible to peeling and the like; accordingly, there are cases in which a desired vibration cannot be generated.
On the other hand, in the shape illustrated in FIG. 8A, the radius R1 of the non-contact portion between the elastic body and the piezoelectric element is determined by the lengths of the contact portion 26 and the connection portion 21.
Now, since both the contact portion 26 and the connection portion 21 deform, different from the shape illustrated in FIG. 8B, in the area of the projection constituting the non-contact portion, there is no portion that does not contribute to reduction of the spring stiffness in the Z direction; accordingly, the radius R1 of the non-contact portion between the elastic body and the piezoelectric element can be reduced.
As a result, the adhesion area between the elastic body and the piezoelectric element can be increased.
Furthermore, when the shape of the projection is integrally formed by press-forming, such as by drawing, since it is easier to carry out processing with a larger draw radius, the shape illustrated in FIG. 8A, in which the length R1 is larger than the length between C and D illustrated in FIG. 8B, can be processed more easily.
The projections of the vibrator and the driven body are in contact with one another intermittently. At this time, since the amplitude of each projection is in the order of micrometers, the contact surface of the driven body and the contact surfaces of the projections need to be smooth surfaces in order to drive the driven body in an accurate manner.
Accordingly, the surfaces of both contact portions are finished to a smooth surface by lapping. As a result, since lapping is performed, the wall thickness of the contact portion becomes thin accordingly.
Now, in the projections illustrated in Japanese Patent Laid-Open No. 2011-234608, because the contact portions are deformed as well upon application of pressure, the spring stiffness changes when the wall thickness of each contact portion decreases.
In order to increase mass productivity, a plurality of elastic bodies need to be lapped at the same time; accordingly, the following issues are encountered.
That is, since the dimension and the warp of each piece of elastic body formed by press working varies, even if lapped in the same manner, the amount of lapping changes by each piece. When the lapping amount varies by each piece, the spring stiffness also varies such that ones with high stiffness and ones with low stiffness are created.
For example, when the lapping amount is small, the stiffness of the projection becomes too high and abnormal noise will be generated during the driving operation and when the lapping is performed excessively, the stiffness of the projection becomes too low and there are cases in which power efficiency and the like decrease. The decrease in the stiffness of the projection also occurs when the contact portion of the projection is worn away after a long period of driving operation.